Experimental And Numerical Simulation Study On Ultrasonic Welding Of 6061 Aluminum Alloy/Steel And 6061 Aluminum/Pure Copper Joints

In order to achieve the"dual carbon"goal including"carbon peaks"and"carbon neutrality",the lightweight of the car has become a hot spot.Reducing the weight of the car will reduce the amount of fuel consumption and CO₂ emissions,thereby effectively reducing pollution to the environment.Aluminum alloy has the advantages of light quality and high strength,and some aluminum alloys can reach the same strength of steel,and can replace steel in the lightweight of the car body.In addition,aluminum and copper are also the main materials for electric vehicle power battery assembly.Because there is a large difference in physical properties between Al/Steel and Al/Cu,it is difficult to weld using traditional welding methods.Ultrasonic welding has the advantages of high efficiency,short welding time,and easy to achieve automation,which is suitable for the welding of Al/Steel and Al/Cu joints.For Al/Steel ultrasonic welding,there are fewer studies,while for Al/Cu ultrasonic welding,the joints strength quality needs to be improved.（1）6061-T6 Al/DC04 low-carbon steel high-power ultrasonic welding was carried out.The microstructures of the welding interface,the plastic deformation of the joints,and the process of growing in the middle are observed by scanning electron microscope and XRD diffraction analysis.6061-T6 Al/DC04 steel ultrasonic welding the mechanical properties and fracture characteristics were investigated.The results show that when the welding pressure is 1980 N and the amplitude is 27μm,obvious plastic deformation and mechanical interlock appears at the interface.The interface is combined with some good metallurgy reactions.The thickness of IMC is 1.7μm,and its chemical composition of Fe₂Al₅ and FeAl₃.The IMC thickness of the welding center is larger than the welding edge.The maximum lap-shear force obtained of joint is 3.95 k N.The fracture characteristics of the interface are composed of brittle and ductility.（2）The high-power ultrasonic welding finite element model of 6061-T6 Al/DC04steel was proposed.The ultrasonic softening of low-carbon steel is considered in this model.The temperature field and plastic strain distribution of materials during the welding process was investigated.The predicted peak temperature is about 566℃.The material of the interface gradually flows from the outer edge of the welding area to its middle area,and then accumulated in a near-shaped zone was about 10 mm×11 mm.The accumulation behavior of materials promotes the formation of the welding interface.（3）Parameters in 6061-T6 Al/pure Cu high-power ultrasonic welding are optimization by basis for the highest penetration depth of the sonotrode tip into upper specimen and lowest penetration depth of the anvil tip into bottom specimen.In addition,the microstructure and joint mechanical properties under the optimization parameter were investigated.The optimized welding parameters are:welding pressure 1450 N,amplitude25μm,and the welding time 0.54 s.The peak temperature of the interface is 442℃.Under the action of temperature and ultrasonic softening,the IMC generation at the interface is about 1.95μm,which is mainly composed of Al₂Cu.The tensile-shear force reaches the maximum value of 3.2 k N.The fracture model is ductile-brittle brid fracture.